U.S. patent application number 11/044087 was filed with the patent office on 2005-08-25 for inkjet recording apparatus.
This patent application is currently assigned to Fuji Photo Film Co., Ltd.. Invention is credited to Nagashima, Kanji.
Application Number | 20050185040 11/044087 |
Document ID | / |
Family ID | 34857620 |
Filed Date | 2005-08-25 |
United States Patent
Application |
20050185040 |
Kind Code |
A1 |
Nagashima, Kanji |
August 25, 2005 |
Inkjet recording apparatus
Abstract
The inkjet recording apparatus comprises: a head which ejects
ink droplets of light-curable ink to a print medium to form an
image on the print medium; a light irradiating device which is
located at a downstream side of the head, and irradiates light from
a light source onto the ink droplets immediately after the ink
droplets have been deposited on the print medium; and a control
device which controls the light irradiating device in such a manner
that luminous energy irradiated onto a region of the print medium
where bleeding of the ink droplets would be conspicuous is greater
than luminous energy irradiated onto another region of the print
medium.
Inventors: |
Nagashima, Kanji;
(Ashigara-Kami-Gun, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
Fuji Photo Film Co., Ltd.
Minami-Ashigara-shi
JP
|
Family ID: |
34857620 |
Appl. No.: |
11/044087 |
Filed: |
January 28, 2005 |
Current U.S.
Class: |
347/102 ;
347/17 |
Current CPC
Class: |
B41J 11/002 20130101;
B41M 7/0081 20130101 |
Class at
Publication: |
347/102 ;
347/017 |
International
Class: |
B41J 029/38 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 30, 2004 |
JP |
2004-23671 |
Claims
What is claimed is:
1. An inkjet recording apparatus, comprising: a head which ejects
ink droplets of light-curable ink to a print medium to form an
image on the print medium; a light irradiating device which is
located at a downstream side of the head, and irradiates light from
a light source onto the ink droplets immediately after the ink
droplets have been deposited on the print medium; and a control
device which controls the light irradiating device in such a manner
that luminous energy irradiated onto a region of the print medium
where bleeding of the ink droplets would be conspicuous is greater
than luminous energy irradiated onto another region of the print
medium.
2. The inkjet recording apparatus as defined in claim 1, wherein
the region of the print medium where the bleeding of the ink
droplets would be conspicuous is at least one of an edge of a solid
print region in the image, an edge of a line region in the image,
an isolated dot in the image, a region of high contrast in the
image, and a region of large color variation in the image.
3. The inkjet recording apparatus as defined in claim 1, wherein:
the light irradiating device includes a scanning device which scans
the print medium in a width direction of the print medium with the
light having a prescribed beam width; and the control device
controls the light irradiating device to irradiate constant
luminous energy, and controls the scanning device in such a manner
that a scanning speed with respect to the region of the print
medium where the bleeding of the ink would be conspicuous is slower
than a scanning speed with respect to the other region of the print
medium.
4. The inkjet recording apparatus as defined in claim 1, wherein:
the light irradiating device includes a scanning device which
two-dimensionally scans the print medium in a width direction and a
conveyance direction of the print medium with the light having a
prescribed beam width; and the control device controls the light
irradiating device to irradiate constant luminous energy, and
controls the scanning device in such a manner that a scanning speed
with respect to the region of the print medium where the bleeding
of the ink would be conspicuous is slower than a scanning speed
with respect to the other region of the print medium.
5. The inkjet recording apparatus as defined in claim 1, wherein:
the light irradiating device includes a scanning device which
two-dimensionally scans the print medium in a width direction and a
conveyance direction of the print medium with the light having a
prescribed beam width; and the control device controls the light
irradiating device to irradiate constant luminous energy, and
controls the scanning device in such a manner that the region of
the print medium where the bleeding of the ink would be conspicuous
is scanned a plurality of times.
6. The inkjet recording apparatus as defined in claim 1, wherein:
the light irradiating device includes a scanning device which
two-dimensionally scans the print medium in a width direction and a
conveyance direction of the print medium with the light having a
prescribed beam width; and the control device controls a scanning
speed of the scanning device to be constant, and controls the light
source of the light irradiating device in such a manner that the
luminous energy irradiated onto the region of the print medium
where the bleeding of the ink would be conspicuous is
increased.
7. The inkjet recording apparatus as defined in claim 1, wherein
the light irradiating device includes a scanning device, including:
the light source which emits the light; an optical system including
a scanning mirror, the optical system concentrating the light
emitted by the light source onto the print medium through the
scanning mirror; and a mirror turning device which turns the
scanning mirror.
8. The inkjet recording apparatus as defined in claim 7, wherein:
the head is a line type head having a length corresponding to a
maximum width of the print medium; and the light irradiating device
comprises a plurality of the scanning devices arranged in a
longitudinal direction of the line type head.
9. The inkjet recording apparatus according to claim 7, further
comprising a print determination device, including: a branching
device which is disposed in an optical path between the light
source and the scanning mirror, and causes reflected light which is
reflected at a focal point of the optical system on the print
medium and returns back through the optical system to branch off;
an optical sensor which measures the reflected light branched off
by the branching device and outputs a measurement signal; and a
judging device which judges whether the ink droplet presents on the
print medium or not according to the measurement signal obtained
from the optical sensor.
10. The inkjet recording apparatus according to claim 7, further
comprising an ink ejection determination device, including: a first
branching device which is disposed in an optical path of the
optical system, and causes the light to branch off in such a manner
that the light passes through a gap between the head and the print
medium, thereby irradiating the light onto the ink droplets which
have been ejected from the head and have not yet been deposited on
the print medium; a second branching device which is disposed in
the optical path between the light source and the scanning mirror,
and causes reflected light reflected by the ink droplets which have
not yet been deposited on the print medium and returned back
through the optical system to branch off; an optical sensor which
measures the reflected light branched off by the second branching
device and outputs a measurement signal; and a judging device which
judges whether the ink droplets have been ejected from nozzles of
the head or not according to the measurement signal obtained from
the optical sensor.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an inkjet recording
apparatus, and more particularly to a technology for preventing ink
from bleeding.
[0003] 2. Description of the Related Art
[0004] Conventional printing processes are well known in which
printing is carried out onto a print medium by employing an
ultraviolet (UV) curable ink, and the ink is prevented from
bleeding by causing the ink to harden by irradiating UV light onto
the ink after the ink has been deposited on the print medium.
[0005] Japanese Patent Application Publication No. 2003-11334
discloses a device in that a UV light source is arranged integrally
with an ink ejecting head along the travel direction of the head.
The ink ejected from the head is caused to harden by irradiating UV
light from the UV light source onto the ink in a recorded region
that has been recorded in the previous scan.
[0006] Japanese Patent Application Publication No. 2003-11343
discloses a technique in that, when an ink ejection operation has
been performed, the ejected ink is hardened by irradiating UV light
before the next ink ejection operation in order to prevent ink
bleeding and recording irregularities.
[0007] In Japanese Patent Application Publication No. 2002-187918,
paragraph "0104", there is a description that the ink should be
caused to harden before the ink permeates into the recording medium
(the recording paper).
[0008] Japanese Patent Application Publication No. 2003-89198
discloses that a light guide that irradiates setting light for
provisional curing is arranged in the vicinity of an inkjet nozzle.
After the ink has been provisionally cured by means of the setting
light from the light guide, the ink is durably fixed by another
light source.
[0009] Japanese Patent Application Publication No. 2003-145741
discloses a fixed UV light source of a size that can cover the
range scanned by a head.
[0010] In Japanese Patent Application Publication No. 2003-192943,
there is a description that a time period from the ink ejection to
the UV irradiation is determined. Japanese Patent Application
Publication No. 2003-192943 also discloses a line type head having
a length corresponding to the maximum width of the print
medium.
[0011] In Japanese Patent Application Publication No. 2003-191594,
there is a description that various irradiation conditions, such as
the light irradiation time, irradiation intensity, irradiation
surface area, and angle of incidence, are adjusted in accordance
with the type of the print medium, the type of the ink, the
viscosity of the ink, and the like.
[0012] Japanese Patent Application Publication No. 60-132767 and
U.S. Pat. No. 6,092,890 disclose a UV light source arranged
integrally with a head.
[0013] U.S. Pat. No. 6,145,979 discloses a device in that light is
guided from the outside of a head to the vicinity of the head
through mirrors or an optical fiber, and the device irradiates the
light with the movement of the head unit.
[0014] The above-described conventional apparatuses are classified
into any one of the followings:
[0015] (1) a light source for curing ink is fixed to an inkjet
recording apparatus, and the light source irradiates light onto the
whole of the irradiation object as the irradiation object
moves;
[0016] (2) a light source for curing ink is fixed to a head, and
the light source irradiates light onto the irradiation object as
the head moves for scan; or
[0017] (3) a light source for curing ink guides light to the head
from the outside of the head through some kind of device and/or
method, and the light source irradiates light onto the irradiation
object as the head moves for scan.
[0018] All of the above-described conventional apparatuses adopt
the same approach in that the light is directed onto the whole of
the print medium. The conventional apparatuses are devised in order
that the light is irradiated as immediately as possible after
printing so that the print ink can be prevented from bleeding. More
specifically, the above-described conventional inkjet recording
apparatuses irradiate UV light immediately after the ink has been
ejected toward the print medium so that the ink is prevented from
bleeding; however, they may involve the following problems.
[0019] (1) In order to irradiate the UV light immediately after the
ink has been ejected, it is necessary to arrange a light source or
a member for guiding the UV light in the vicinity of the head. When
the UV light is to be irradiated onto the entire print region for
causing the ink to harden, high energy is required and hence the
light source unit can be large in size.
[0020] (2) When the UV light is irradiated onto the print medium,
the UV light can reach the peripheral areas by the diffuse
reflection at the irradiation position. If the irradiation position
of the UV light is brought close to the print position so that the
ink can be prevented from bleeding, the diffuse reflected UV light
may cause the ink to harden inside the head before the ink is
ejected. Thus, there is a possibility of head blockages.
[0021] (3) If a laser diode having good light emission efficiency
is used in order to save energy in the inkjet recording apparatus,
there is a possibility that the energy may not be sufficient to
cause the ink to harden over the whole print medium depending on
the speed of conveyance of the print medium, since the luminous
energy emitted from the laser diode may be smaller than that from
other devices, such as an electric discharge tube.
SUMMARY OF THE INVENTION
[0022] The present invention has been made in view of foregoing
circumstances, and it is an object of the invention to provide an
inkjet recording apparatus that can effectively prevent the ink
from bleeding with a small total luminous energy, accordingly the
light source unit can be compact and the head blockages can be
prevented. Furthermore, it is another object of the invention to
provide an inkjet recording apparatus that can determine the ink
which is ejected from the head by the same optical system as that
used to harden the ink.
[0023] In order to attain the aforementioned object, the present
invention is directed to an inkjet recording apparatus, comprising:
a head which ejects ink droplets of light-curable ink to a print
medium to form an image on the print medium; a light irradiating
device which is located at a downstream side of the head, and
irradiates light from a light source onto the ink droplets
immediately after the ink droplets have been deposited on the print
medium; and a control device which controls the light irradiating
device in such a manner that luminous energy irradiated onto a
region of the print medium where bleeding of the ink droplets would
be conspicuous is greater than luminous energy irradiated onto
another region of the print medium.
[0024] According to the present invention, as the light is
intensively irradiated onto the region where the bleeding of the
ink would be conspicuous, it is possible to effectively prevent the
bleeding of the ink and to reduce the total luminous energy
irradiated onto the print medium.
[0025] Preferably, the region of the print medium where the
bleeding of the ink droplets would be conspicuous is at least one
of an edge of a solid print region in the image, an edge of a line
region in the image, an isolated dot in the image, a region of high
contrast in the image, and a region of large color variation in the
image.
[0026] Preferably, the light irradiating device includes a scanning
device which scans the print medium in a width direction of the
print medium with the light having a prescribed beam width; and the
control device controls the light irradiating device to irradiate
constant luminous energy, and controls the scanning device in such
a manner that a scanning speed with respect to the region of the
print medium where the bleeding of the ink would be conspicuous is
slower than a scanning speed with respect to the other region of
the print medium.
[0027] According to the present invention, the light irradiating
device has the scanning device which scans the print medium in the
width direction of the print medium with the light of the
prescribed beam width. Rather than adopting a constant scanning
speed in the scanning device, the scanning speed is slowed with
respect to the region where the bleeding of the ink would be
conspicuous and the scanning speed is raised in the other regions.
Thereby, the light is intensively irradiated onto the region where
the bleeding of the ink would be conspicuous.
[0028] Alternatively, it is also preferable that the light
irradiating device includes a scanning device which
two-dimensionally scans the print medium in a width direction and a
conveyance direction of the print medium with the light having a
prescribed beam width; and the control device controls the light
irradiating device to irradiate constant luminous energy, and
controls the scanning device in such a manner that a scanning speed
with respect to the region of the print medium where the bleeding
of the ink would be conspicuous is slower than a scanning speed
with respect to the other region of the print medium.
[0029] Alternatively, it is also preferable that the light
irradiating device includes a scanning device which
two-dimensionally scans the print medium in a width direction and a
conveyance direction of the print medium with the light having a
prescribed beam width; and the control device controls the light
irradiating device to irradiate constant luminous energy, and
controls the scanning device in such a manner that the region of
the print medium where the bleeding of the ink would be conspicuous
is scanned a plurality of times.
[0030] If the region where the bleeding of the ink would be
conspicuous extends in the width direction of the print medium,
then a long time is required to perform one scan if the scanning
speed is slowed in this region. Hence, there is a possibility that
irradiation misses may occur depending on the size of the beam and
the speed of the conveyance of the print medium. According to the
present invention, rather than reducing the scanning speed
significantly, the same location is scanned a plurality of times
while altering the orientation of the beam at each scan. Thereby,
the light is intensively irradiated onto the region where the
bleeding of the ink would be conspicuous.
[0031] Alternatively, it is also preferable that the light
irradiating device includes a scanning device which
two-dimensionally scans the print medium in a width direction and a
conveyance direction of the print medium with the light having a
prescribed beam width; and the control device controls a scanning
speed of the scanning device to be constant, and controls the light
source of the light irradiating device in such a manner that the
luminous energy irradiated onto the region of the print medium
where the bleeding of the ink would be conspicuous is
increased.
[0032] According to the present invention, the light scanning speed
of the scanning device is set to the constant speed, and the
luminous energy emitted from the light source is adjusted (more
specifically, the luminous energy is changed so that the irradiated
luminous energy can be greater at the region where the bleeding of
the ink would be conspicuous).
[0033] Preferably, the light irradiating device includes a scanning
device, including: the light source which emits the light; an
optical system including a scanning mirror, the optical system
concentrating the light emitted by the light source onto the print
medium through the scanning mirror; and a mirror turning device
which turns the scanning mirror.
[0034] For example, the head is a line type head having a length
corresponding to a maximum width of the print medium; and the light
irradiating device comprises a plurality of the scanning devices
arranged in a longitudinal direction of the line type head. The
number of the scanning devices is set according to the width that
can be scanned by each of the scanning devices and the length of
the line type head.
[0035] Preferably, the inkjet recording apparatus further comprises
a print determination device, including: a branching device which
is disposed in an optical path between the light source and the
scanning mirror, and causes reflected light which is reflected at a
focal point of the optical system on the print medium and returns
back through the optical system to branch off; an optical sensor
which measures the reflected light branched off by the branching
device and outputs a measurement signal; and a judging device which
judges whether the ink droplet presents on the print medium or not
according to the measurement signal obtained from the optical
sensor.
[0036] According to the present invention, the optical system of
the light irradiating device is utilized to branch off the light
irradiated toward and reflected by the ink droplets so as to direct
the reflected light to the optical sensor. It is then judged
whether the ink droplets have been deposited or not according to
the measurement signal outputted from the optical sensor. The
reflected light includes the light based on mirror reflection and
the light based on diffuse reflection.
[0037] Alternatively, it is also preferable that the inkjet
recording apparatus further comprises an ink ejection determination
device, including: a first branching device which is disposed in an
optical path of the optical system, and causes the light to branch
off in such a manner that the light passes through a gap between
the head and the print medium, thereby irradiating the light onto
the ink droplets which have been ejected from the head and have not
yet been deposited on the print medium; a second branching device
which is disposed in the optical path between the light source and
the scanning mirror, and causes reflected light reflected by the
ink droplets which have not yet been deposited on the print medium
and returned back through the optical system to branch off; an
optical sensor which measures the reflected light branched off by
the second branching device and outputs a measurement signal; and a
judging device which judges whether the ink droplets have been
ejected from nozzles of the head or not according to the
measurement signal obtained from the optical sensor.
[0038] According to the present invention, utilizing the optical
system of the light irradiating device, the light is branched off
by means of the first branching device situated in the optical path
of the optical system, in such a manner that the light passes
through the gap between the head and the print medium and is
directed onto the ink droplets that have been ejected from the head
and have not yet been deposited on the print medium. The light
irradiated toward and reflected by the ink droplets returns through
the same optical system, is branched by the second branching
device, and is directed to the optical sensor. It is then judged
whether the ink droplets have been ejected from the nozzles of the
head or not according to the measurement signal outputted from the
optical sensor.
[0039] According to the present invention, it is possible to reduce
the total luminous energy irradiated onto the print medium and
effectively prevent the bleeding of the ink, since the light is
intensively irradiated onto the region where the bleeding of the
ink would be conspicuous, such as the edges of the solid print
region, the edges of the line region, the isolated dots, the
regions of high contrast, and the regions of large color variation.
Furthermore, it is possible that the light source unit can be more
compact and the head blockages can be prevented by restricting the
total luminous energy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] The nature of this invention, as well as other objects and
advantages thereof, will be explained in the following with
reference to the accompanying drawings, in which like reference
characters designate the same or similar parts throughout the
figures and wherein:
[0041] FIG. 1 is a general schematic drawing of an inkjet recording
apparatus according to an embodiment of the present invention;
[0042] FIG. 2 is a block diagram of principal components showing
the system composition of the inkjet recording apparatus;
[0043] FIG. 3 is a perspective view of a print unit having an
integrally installed UV laser scanner;
[0044] FIG. 4 is a diagram showing the internal composition of the
UV laser scanner;
[0045] FIGS. 5A and 5B are schematic drawings of the optical system
of the UV laser scanner;
[0046] FIG. 6 is a diagram for describing a UV light irradiating
unit in the UV laser scanner;
[0047] FIGS. 7A, 7B, and 7C are diagrams for describing a method
for irradiating UV light intensively onto the region of the
recording paper where the bleeding of the ink would be
conspicuous,
[0048] FIGS. 8A and 8B are diagrams for describing a further method
for irradiating UV light intensively onto the region of the
recording paper where the bleeding of the ink would be
conspicuous;
[0049] FIGS. 9A, 9B, 9C, and 9D are diagrams for describing the
details of the timing at which the scanning speed of the UV light
is changed;
[0050] FIG. 10 is a side view of the vicinity of a head in order to
describe a method for determining the ink ejection by using the
scanning optical system of the UV laser scanner;
[0051] FIGS. 11A, 11B, and 11C are diagrams showing the UV laser
scanner installed integrally in a shuttle type head; and
[0052] FIGS. 12A, 12B, and 12C are diagrams showing the Prewitt
matrix, the Sobel matrix and the Roberts matrix for edge
detection.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0053] First, the description of an inkjet recording apparatus
according to the present invention is explained. FIG. 1 is a
general schematic drawing of an inkjet recording apparatus for
forming an image by ejecting inks as droplet onto a recording
medium, according to an embodiment of the present invention. As
shown in FIG. 1, the inkjet recording apparatus 10 comprises: a
printing unit 12 having a plurality of inkjet heads (hereinafter
referred to as "head" simply) 12K, 12C, 12M, and 12Y for ink colors
of black (K), cyan (C), magenta (M), and yellow (Y), respectively;
an ink storing/loading unit 14 for storing inks to be supplied to
the print heads 12K, 12C, 12M, and 12Y; a paper supply unit 18 for
supplying recording paper 16; a decurling unit 20 for removing curl
in the recording paper 16; a suction belt conveyance unit 22
disposed facing the nozzle face (ink-droplet ejection face) of the
print unit 12, for conveying the recording paper 16 while keeping
the recording paper 16 flat; a print determination unit 24 for
reading the printed result produced by the printing unit 12; and a
paper output unit 26 for outputting image-printed recording paper
(printed matter) to the exterior.
[0054] The recording paper 16 delivered from the paper supply unit
18 retains curl due to having been loaded in the magazine. In order
to remove the curl, heat is applied to the recording paper 16 in
the decurling unit 20 by a heating drum 30 in the direction
opposite from the curl direction in the magazine. The heating
temperature at this time is preferably controlled so that the
recording paper 16 has a curl in which the surface on which the
print is to be made is slightly round outward.
[0055] In the case of the configuration in which roll paper is
used, a cutter (first cutter) 28 is provided as shown in FIG. 1,
and the continuous paper is cut into a desired size by the cutter
28. The cutter 28 has a stationary blade 28A, of which length is
equal to or greater than the width of the conveyor pathway of the
recording paper 16, and a round blade 28B, which moves along the
stationary blade 28A. The stationary blade 28A is disposed on the
reverse side of the printed surface of the recording paper 16, and
the round blade 28B is disposed on the printed surface side across
the conveyor pathway. When cut paper is used, the cutter 28 is not
required.
[0056] The decurled and cut recording paper 16 is delivered to the
suction belt conveyance unit 22. The suction belt conveyance unit
22 has a configuration in which an endless belt 33 is set around
rollers 31 and 32 so that the portion of the endless belt 33 facing
at least the nozzle face of the printing unit 12 and the sensor
face of the print determination unit 24 forms a horizontal plane
(flat plane).
[0057] The belt 33 has a width that is greater than the width of
the recording paper 16, and a plurality of suction apertures (not
shown) are formed on the belt surface. A suction chamber 34 is
disposed in a position facing the sensor surface of the print
determination unit 24 and the nozzle surface of the printing unit
12 on the interior side of the belt 33, which is set around the
rollers 31 and 32, as shown in FIG. 1; and the suction chamber 34
provides suction with a fan 35 to generate a negative pressure, and
the recording paper 16 is held on the belt 33 by suction.
[0058] The belt 33 is driven in the clockwise direction in FIG. 1
by the motive force of a motor (not shown) being transmitted to at
least one of the rollers 31 and 32, which the belt 33 is set
around, and the recording paper 16 held on the belt 33 is conveyed
from left to right in FIG. 1.
[0059] Since ink adheres to the belt 33 when a marginless print job
or the like is performed, a belt-cleaning unit 36 is disposed in a
predetermined position (a suitable position outside the printing
area) on the exterior side of the belt 33.
[0060] A heating fan 40 is disposed on the upstream side of the
printing unit 12 in the conveyance pathway formed by the suction
belt conveyance unit 22. The heating fan 40 blows heated air onto
the recording paper 16 to heat the recording paper 16 immediately
before printing so that the ink deposited on the recording paper 16
dries more easily.
[0061] The printing unit 12 forms a so-called full-line head in
which a line head having a length that corresponds to the maximum
paper width is disposed in the main scanning direction
perpendicular to the delivering direction of the recording paper
16, which is substantially perpendicular to a width direction of
the recording paper 16. Each of the print heads 12K, 12C, 12M, and
12Y is composed of a line head, in which a plurality of ink-droplet
ejection apertures (nozzles) are arranged along a length that
exceeds at least one side of the maximum-size recording paper 16
intended for use in the inkjet recording apparatus 10.
[0062] The print heads 12K, 12C, 12M, and 12Y are arranged in this
order from the upstream side along the delivering direction of the
recording paper (hereinafter referred to as the paper conveyance
direction). A color print can be formed on the recording paper 16
by ejecting the inks from the print heads 12K, 12C, 12M, and 12Y,
respectively, onto the recording paper 16 while conveying the
recording paper 16.
[0063] The print determination unit 24 has a line sensor for
capturing an image of the ink-droplet deposition result of the
print unit 12, and functions as a device to check for ejection
defects such as clogs of the nozzles in the print unit 12 from the
ink-droplet deposition results evaluated by the line sensor.
[0064] A post-drying unit 42 is disposed following the print
determination unit 24. The post-drying unit 42 is a device to dry
the printed image surface, and includes a heating fan, for example.
It is preferable to avoid contact with the printed surface until
the printed ink dries, and a device that blows heated air onto the
printed surface is preferable.
[0065] A heating/pressurizing unit 44 is disposed following the
post-drying unit 42. The heating/pressurizing unit 44 is a device
to control the glossiness of the image surface, and the image
surface is pressed with a pressure roller 45 having a predetermined
uneven surface shape while the image surface is heated, and the
uneven shape is transferred to the image surface.
[0066] The printed matter generated in this manner is outputted
from the paper output unit 26. The target print (i.e., the result
of printing the target image) and the test print are preferably
outputted separately. In the inkjet recording apparatus 10, a
sorting device (not shown) is provided for switching the outputting
pathway in order to sort the printed matter with the target print
and the printed matter with the test print, and to send them to
paper output units 26A and 26B, respectively. When the target print
and the test print are simultaneously formed in parallel on the
same large sheet of paper, the test print portion is cut and
separated by a cutter (second cutter) 48. The cutter 48 is disposed
directly in front of the paper output unit 26, and is used for
cutting the test print portion from the target print portion when a
test print has been performed in the blank portion of the target
print. The structure of the cutter 48 is the same as the first
cutter 28 described above, and has a stationary blade 48A and a
round blade 48B.
[0067] FIG. 2 is a principal block diagram showing the system
configuration of the inkjet recording apparatus 10.
[0068] The inkjet recording apparatus 10 has a UV laser scanner 60,
a communication interface 70, a system controller 72, an image
memory 74, a motor driver 76, a heater driver 78, a print
controller 80, an image buffer memory 82, a head driver 84, and
other components.
[0069] The UV laser scanner 60 makes UV curable inks harden by
irradiating UV light to the ink droplets deposited on the recording
paper 16 for preventing the ink from bleeding. A specific
structural example of the UV laser scanner 60 is described
later.
[0070] The communication interface 70 is an interface unit for
receiving image data sent from a host computer 86. A serial
interface such as USB, IEEE1394, Ethernet, wireless network, or a
parallel interface such as a Centronics interface may be used as
the communication interface 70. A buffer memory (not shown) may be
mounted in this portion in order to increase the communication
speed. The image data sent from the host computer 86 is received by
the inkjet recording apparatus 10 through the communication
interface 70, and is temporarily stored in the image memory 74. The
image memory 74 is a storage device for temporarily storing images
inputted through the communication interface 70, and data is
written and read to and from the image memory 74 through the system
controller 72. The image memory 74 is not limited to memory
composed of a semiconductor element, and a hard disk drive or
another magnetic medium may be used.
[0071] The system controller 72 controls the communication
interface 70, image memory 74, motor driver 76, heater driver 78,
and other components. The system controller 72 has a central
processing unit (CPU), peripheral circuits therefore, and the like.
The system controller 72 controls communication between itself and
the host computer 86, controls reading and writing from and to the
image memory 74, and performs other functions, and also generates
control signals for controlling the motor 88 and a heater 89 in the
conveyance system.
[0072] The motor driver (the drive circuit) 76 drives the motor 88
in accordance with commands from the system controller 72. The
heater driver (drive circuit) 78 drives the heater 89 of the
post-drying unit 42 or the like in accordance with commands from
the system controller 72.
[0073] The print controller 80 has a signal processing function for
performing various tasks, compensations, and other types of
processing for generating print control signals from the image data
stored in the image memory 74 in accordance with commands from the
system controller 72 so as to apply the generated print control
signals (image formation data) to the head driver 84. Prescribed
signal processing is carried out in the print control unit 80, and
the ejection amount and the ejection timing of the ink droplets or
the protective liquid from the respective print heads 50 are
controlled via the head driver 84, on the basis of the image data.
By this means, prescribed dot size, dot positions, or coating of
protective liquid can be achieved.
[0074] As described later, the print controller 80 has functions
for controlling the UV laser scanner 60 to prevent the ink
bleeding, and for determining the printing and the ink ejection
according to determination signals inputted from the UV laser
scanner 60.
[0075] The print controller 80 is provided with the image buffer
memory 82; and image data, parameters, and other data are
temporarily stored in the image buffer memory 82 when image data is
processed in the print controller 80. The aspect shown in FIG. 2 is
one in which the image buffer memory 82 accompanies the print
controller 80; however, the image memory 74 may also serve as the
image buffer memory 82. Also possible is an aspect in which the
print controller 80 and the system controller 72 are integrated to
form a single processor.
[0076] The head driver 84 drives the actuators 59 for the print
heads 12K, 12C, 12M and 12Y of the respective colors on the basis
of the print data received from the print controller 80. A feedback
control system for keeping the drive conditions for the print heads
constant may be included in the head driver 84.
[0077] As shown in FIG. 1, the print determination unit 24 is a
block including the line sensor. The print determination unit 24
scans the image printed on the recording paper 16, performs various
signal processing operations and the like, and determines the print
situation (e.g., whether the ink has been ejected or not, variation
in the ink droplet ejection, etc.). Then, the print determination
unit 24 supplies these determination results to the print control
unit 80. Furthermore, as circumstances demand, the print controller
80 makes various corrections with respect to the print unit 12
according to information obtained from the print determination unit
24.
[0078] Next, the UV laser scanner 60 is described.
[0079] The inks of various colors, namely black (K), cyan (C),
magenta (M) and yellow (Y) in the ink storing and loading unit 14
are UV curable inks, which are harden when exposed to UV light.
Each of the heads 12K, 12C, 12M, 12Y, which ejects the ink of a
particular color, is provided with a UV laser scanner 60.
[0080] FIG. 3 is a perspective diagram of the head 12K and the UV
laser scanner 60, which is integrally arranged on the head 12K.
[0081] As shown in FIG. 3, the UV laser scanner 60 comprises three
scanners 60A, 60B and 60C. The number of scanners, constituting the
UV laser scanner 60 corresponding to each head, is not limited to
three, and may be set in accordance with the width of the head and
the width of the scan performed by one scanner.
[0082] The recording paper (the printing paper) 16 is a paper of
the maximum width that can be printed by using the head 12. The UV
laser scanner 60 is able to scan the entire width of the recording
paper 16 by means of UV light.
[0083] The head 12K is connected to a flexible wiring board 13A for
driving and controlling each of actuators on nozzles in the head
12K. The head 12K is also connected to pipes 13B for supplying
black (K) ink to the head 12K. The scanners 60A, 60B and 60C are
connected to flexible wiring boards 15A, 15B and 15C, through which
signals for controlling the operation of the scanners 60A, 60B and
60C are applied to the respective scanners, and determination
signals from optical sensors (described hereafter) in the scanners
60A, 60B and 60C are outputted. A UV lamp 17 is fixed to a
prescribed position corresponding to the downstream side of the
recording paper 16 fed in the direction of arrow A, and is capable
of simultaneously irradiating the UV light across the entire width
of the recording paper 16.
[0084] FIG. 4 is a diagram showing the internal composition of the
scanners 60A, 60B, and 60C of the UV laser scanner 60, the diagram
being relevant to the scanner 60A as an example.
[0085] As shown in FIG. 4, the scanner 60A principally comprises a
UV laser light source (e.g., a UV laser diode) 61, a collimator
lens 62, a cylindrical lens 63, a scanning mirror 67, and a
condenser mirror 69. The scanner 60A further comprises: a
semitransparent mirror (or a polarization mirror) 64 arranged in
the light path between the cylindrical lens 63 and the scanning
mirror 67; a condenser lens 65 for concentrating the light branched
off by the semitransparent mirror 64; and an optical sensor 66,
such as a photodiode, for determining the light concentrated by the
condenser lens 65.
[0086] FIGS. 5A and 5B are schematic drawings of the optical system
of the scanner 60A in the xz plane and the yz plane, respectively.
As shown in FIG. 4, the x direction is the longitudinal direction
of the head 12K, which is the scanning direction of the UV light.
The z direction is the direction of the optical axis of the optical
system of the scanner 60A. The y direction is the direction
orthogonal to both the x and z directions.
[0087] UV light emitted from the UV laser light source 61 is
converted into parallel light by the collimator lens 62, and then
enters the cylindrical lens 63. The parallel light incident on the
cylindrical lens 63 is concentrated in the y direction by the
cylindrical lens 63, and then enters the semitransparent mirror 64,
the scanning mirror 67, and the condenser mirror 69. The UV laser
light incident on the condenser mirror 69 is concentrated in the x
and y directions by the condenser mirror 69. The UV light emitted
from the UV laser light source 61 is concentrated into the UV light
of a prescribed size on the recording paper 16 through this optical
system. In the optical system of the scanner 60A, the light
emission point of the UV laser light source 61 is conjugate with
the light concentrating point on the recording paper 16.
[0088] The size of the UV light concentrated on the recording paper
16 is required to be larger than the print size of one dot of the
ink (for example, 25 .mu.m in diameter). The exact size to which
the UV light concentrated on the recording paper 16 is preferably
set varies depending on the characteristics of the ink and the
print medium. In the case of the combination of the ink and the
print medium that is highly prone to lead to the bleeding of the
ink, it is desirable that UV light be irradiated over the broader
width on the recording paper 16. In the case of the combination of
a standard paper and a standard ink property, it is desirable that
the irradiated UV light has a width of approximately 0.1 mm to 0.5
mm on the recording paper 16. The condenser mirror 69 may or may
not have the f.theta. characteristics and the sin .theta.
characteristics, and the scanning line may not be linear.
[0089] The scanning mirror 67 is arranged turnably on an axis in
the y direction as shown in FIG. 4. The scanning mirror 67 is
turned to a desired angle by means of a mirror driver 68, which is
driven by electrostatic force, electromagnetic force, or the like.
By controlling the angle of the scanning mirror 67 according to a
command from the print controller 80, the UV light concentrated on
the recording paper 16 can be irradiated to scan in the x
direction, which is the width direction of the recording paper 16.
In this case, since the UV laser scanner 60 is not used to actually
record images, it is not necessary to perform the scanning in high
accuracy (high accuracy of position) as in the case of a general
laser printer. A suitable scanning accuracy may be set in
accordance with the size of the irradiated UV light, the conveyed
speed of the print medium, and the amount of movement of the print
medium determined from the time required to perform one scan so
that the irradiation miss concerning the ink droplets that require
irradiation does not arise.
[0090] Next, a method of preventing bleeding of ink according to
the present embodiment of the present invention is described.
[0091] FIG. 6 shows a recording paper 16 after irradiation with the
UV light by the UV laser scanner 60. The thick lines in FIG. 6
represent regions irradiated with the UV light by the UV laser
scanner 60.
[0092] In the present embodiment, immediately after printing, the
UV light is concentrated and irradiated by the UV laser scanner 60
onto regions where bleeding of ink would be conspicuous, such as
edges of a solid print region 16A, edges of a line region 16B, and
an isolated dot 16C on the recording paper 16. After that, the UV
lamp 17 is used for irradiating the UV light onto the whole region
of the recording paper 16 so that the ink can be hardened, as shown
in FIG. 3.
[0093] Next, a method for irradiating the UV light intensively onto
the regions of the recording paper 16 where the bleeding of the ink
would be conspicuous is described.
[0094] As shown in FIG. 7A, when the UV light is intensively
irradiated onto the edges of the solid print region 16A by the UV
laser scanner 60 while the solid print region 16A is being printed,
the scanning speed of the UV light in the x direction, which is the
width direction of the recording paper 16, is varied depending on
the scanning position as shown in FIG. 7B so as to be adjusted to a
low speed only when the UV light is being irradiated onto the edges
of the solid print region 16A. In this case, the luminous energy of
the UV light emitted from the UV laser light source 61 is
constant.
[0095] On the other hand, it is possible that the scanning speed of
the UV laser scanner 60 is constant, and that the luminous energy
of the UV light emitted from the UV laser light source 61 is
changeable as shown in FIG. 7C. The luminous energy is adjusted to
a maximum when the UV light is being irradiated onto the edges of
the solid print region 16A, whereas the luminous energy is reduced
to the luminous energy of a bias level when the UV light is being
irradiated onto other regions of the recording paper 16. The
luminous energy is reduced to a bias level in FIG. 7C with respect
to the regions other than the border regions, whereas the UV laser
light source 61 can be turned off with respect to the regions other
than the border regions.
[0096] The scanner 60A shown in FIG. 4 performs one-dimensional
scanning with the UV light. It is also possible to adopt a
configuration in which the scanning mirror 67 is also tunable on an
axis in the x direction so that the scanner 60A can perform
two-dimensional scanning.
[0097] Next, a method for scanning with the UV light by means of a
scanner capable of two-dimensional scanning is described.
[0098] In FIG. 8A, print regions 16D and 16E printed on the
recording paper 16 have long edges in the direction orthogonal to
the x direction, and a print region 16F has a long edge in the x
direction.
[0099] If the UV light is intensively irradiated onto the edges of
the print regions 16D, 16E and 16F, then when the UV light is
irradiated onto the edges of the print regions 16D and 16E that are
orthogonal to the x direction, the scanning speed is adjusted to a
low speed, as shown in FIG. 8B.
[0100] On the other hand, when the UV light is irradiated onto the
edge of the print region 16F that is parallel to the x direction,
the scanning speed of the UV light is adjusted to a high speed, as
shown in FIG. 8B. Although the high speed is set in FIG. 8B at a
speed slower than the maximum scanning speed and faster than the
speed during low-speed scanning, the high speed may be equal to the
maximum scanning speed.
[0101] Furthermore, when the UV light is irradiated over the edge
of the print section 16F that is parallel to the x direction, the
UV light is irradiated with the high speed scanning as mentioned
above, and is irradiated a plurality of times by means of a
plurality of scanning operations. While the recording paper 16 is
conveyed and thereby moves during the plurality of scanning
operations, the UV light is irradiated onto the same edge by
changing the irradiation direction of the UV light (specifically,
changing the turn angle of the scanning mirror 67 on the x
direction axis) according to the movement of the recording paper
16.
[0102] Consequently, it is possible to irradiate the UV light
intensively onto the edge that is parallel to the x direction.
Furthermore, even when the UV light is irradiated onto a long edge
that is parallel to the x direction, it is possible to prevent the
amount of time required to perform one scan in the x direction from
becoming long.
[0103] In this way, the UV laser scanner capable of performing
two-dimensional scanning is able to irradiate UV light efficiently
onto the region where the bleeding of the ink would be
conspicuous.
[0104] At the edges of print regions where the bleeding of the ink
would be conspicuous, it is necessary to ensure that the ink that
has been deposited on the recording paper is reliably hardened with
respect to each dot. The timing at which UV light is intensively
irradiated onto ink droplets is described in more detail.
[0105] FIG. 9A is a diagram showing an arrangement of dots based on
image data. In this example shown in FIG. 9A, the dot pitch is 2400
dots per inch (dpi). At 2400 dpi, the interval between the dots is
10.6 .mu.m.
[0106] FIG. 9B shows the deposited (ejected) state of the ink
droplets corresponding to the dots in FIG. 9A. The diameter of the
ink droplet is 25 .mu.m, which is larger than the size of the dot
having no interval between them based on the image data, and the
ink droplets that are adjacently positioned partially overlap each
other.
[0107] FIG. 9C shows UV light irradiation regions, to which the UV
light requires irradiated to harden the ink droplets shown in FIG.
9B.
[0108] FIG. 9D shows the scanning speed in a case where the UV
light is intensively irradiated onto the irradiation regions shown
in FIG. 9C.
[0109] As shown in FIG. 9D, the scanning speed of the UV light is
adjusted to a low speed just before the scan enters the irradiation
region, and the scanning speed of the UV light is adjusted to a
high speed after the scan leaves the irradiation region. Thereby,
it is possible to reliably harden the ink droplets in the edge of
the print region.
[0110] Although the scanner 60A shown in FIG. 4 has one UV laser
light source 61, it is also possible to use a plurality of UV laser
light sources in one scanner so as to scan with a plurality of UV
light beams. Furthermore, the optical axis of the scanner may be
incident on the recording paper perpendicularly or out of
perpendicularly. If the optical axis of the scanner is incident
perpendicularly on the recording paper, it is possible to obtain a
greater luminous energy (and a greater signal) in the case of print
determination described hereafter. If the optical axis of the
scanner is incident on the recording paper out of perpendicularly,
it is preferable that the optical axis is inclined in a direction
away from the head in such a manner that the diffuse reflected
light reaching the head becomes weaker, so that it is possible to
reduce problems caused by ink hardening inside the head.
[0111] Next, a print determination method using the scanning
optical system of the scanner shown in FIGS. 4, 5A and 5B is
described.
[0112] As described above, the UV light is irradiated onto the ink
droplets ejected and deposited onto the recording paper 16 in order
to harden the ink droplets. This UV light is also diffuse-reflected
at the focal point on the recording paper 16, and the reflected
light passes back through the optical system of the scanner in the
opposite direction to the direction of the irradiation.
[0113] The semitransparent mirror 64 shown in FIGS. 4, 5A and 5B
branches off the reflected light returned through the scanning
optical system of the scanner, and causes the reflected light to
enter the condenser lens 65. The condenser lens 65 concentrates the
incident reflected light on the light receiving surface of the
optical sensor 66.
[0114] The optical sensor 66 outputs, to the print controller 80,
an electrical signal (a measurement signal) corresponding to the
luminous energy of the incident reflected light. The reflectivity
of the surface of the recording paper 16 is different from the
reflectivity of the surface of the ink droplet deposited on the
recording paper 16, and then the luminous energy of the reflected
light when the UV light is irradiated on the ink droplet is
different from the luminous energy of the reflected light when the
UV light is not irradiated on the ink droplet. Accordingly, the
levels of the measurement signals obtained by the optical sensor 66
differ with respect to the surface of the recording paper 16 and
the surface of the ink droplet.
[0115] Hence, the print controller 80 is able to determine the
presence or the absence of the ink droplet according to the
measurement signal obtained from the optical sensor 66. More
specifically, the print controller 80 is able to determine the ink
droplet ejection and deposition results throughout the entire width
direction of the recording paper 16 by taking in the measurement
signal from the optical sensor 66 in synchronism with the scanning
position of the UV light.
[0116] The inkjet recording apparatus 10 according to the present
embodiment comprises the print determination unit 24 having the
line sensor. It is also possible to use the above-described print
determination device that uses the scanning optical system of the
scanner instead of the print determination unit 24.
[0117] Next, an ink ejection determination method using the
scanning optical system of the scanner shown in FIGS. 4, 5A and 5B
is described.
[0118] FIG. 10 is a side view of the vicinity of the head. In order
to achieve this ink ejection determining method, a semitransparent
mirror (or a polarizing mirror) 71 is arranged in the light path
between the condenser mirror 69 of the scanner 60A and the focal
point on the recording paper 16.
[0119] The UV light transmitted through the semitransparent mirror
71 is irradiated onto the ink that has been deposited on the
recording paper 16, and the UV light reflected by the
semitransparent mirror 71 is bent so as to be parallel with the
recording paper 16 in such a manner that the UV light is irradiated
onto an ink droplet 73 that has been ejected from the head 12K and
has not yet been deposited on the recording paper 16.
[0120] When the ink is ejected from the nozzle of the head 12K and
then the UV light is irradiated onto the ink droplet 73 in flight,
the light reflected by the ink droplet 73 returns back in the
opposite direction to the irradiation direction via the
semitransparent mirror 71 and the optical system of the
scanner.
[0121] The light, reflected by the ink droplet 73 and returning via
the scanning optical system of the scanner, can be measured by the
optical sensor 66 in a manner similar to the print determination
operation described above. The print controller 80 is thus able to
determine whether the ink has been ejected from the nozzle or not
with respect to each of the nozzles of the head according to the
measurement signal obtained from the optical sensor 66.
[0122] According to the above-described ink ejection determination
method, it is possible to check for the blockage of the nozzles or
the like without printing onto the recording paper.
[0123] The present embodiments are described with respect to the
inkjet recording apparatus having the line type head, whereas the
present invention is not limited to the present embodiments. The
present invention may also be applied to an inkjet recording
apparatus having a shuttle type head, which reciprocates in a
direction orthogonal to the direction of the conveyance of the
recording paper.
[0124] FIGS. 11A, 11B, and 11C show a UV laser scanner 92
integrally arranged in a shuttle type head 90.
[0125] The irradiation position of the UV light irradiated by the
UV laser scanner 92 moves with the movement of the head 90. When
the UV light is to be intensively irradiated onto the edges of the
print region where the bleeding of the ink would be conspicuous,
then the irradiation position of the UV light emitted from the UV
laser scanner 92 is changed according to the movement of the head
90, as shown in FIGS. 11A, 11B and 11C, and the movement of the
irradiation position of the UV light is halted at the edge of the
print region and/or the movement speed (the scanning speed) of the
irradiation position is reduced at the edge of the print region.
The UV laser scanner 92 may have a similar composition to that
illustrated in FIG. 4. Furthermore, if there are a plurality of
nozzles in the shuttle type head 90, then the UV laser scanner 92
is configured to two-dimensionally scan the ejection positions of
the nozzles with the UV light.
[0126] The above-mentioned embodiments are described with respect
to a case where the inks are the UV curable inks hardened by
irradiating UV light onto the UV curable ink, whereas the present
invention is not limited to this. In the case of using another
radiation-curable or light-curable ink that is hardened by another
type of radiation (e.g., infrared light, visible light, or other
types of radiation) other than the UV light, it is necessary to
irradiate the type of radiation that can harden that ink.
[0127] Moreover, the regions where the ink bleeding would be
conspicuous are not limited to the edges of the solid print region
16A, the edges of the line region 16B, and the isolated dot 16C. A
region of high contrast or a region of large color variation may
also correspond to the region where ink bleeding would be
conspicuous.
[0128] The region of high contrast or the region of large color
variation here is determined as follows, for example. The image to
be printed is expressed as two-dimensional data by means of a
standard color representation method, which uses RGB data, CMYK
data, L*a*b* data, or the like. The two-dimensional data is then
filtered by multiplying the two-dimensional data by an edge
detection matrix such as the Prewitt matrix, the Sobel matrix and
the Roberts matrix. Regions corresponding to higher values out of
values based on the filtering operation results are the edge
region, and are the regions of the high contrast or the large color
variation.
[0129] If emphasis is particularly placed on the contrast, then the
L* data are preferably used. If emphasis is particularly placed on
the color, then a*b* data are preferably used. The method is not
limited to this, and the data based on any type of color
representation methods may be used.
[0130] Instead of using the matrix for the edge detection, it is
also possible to derive the absolute values for the concentration
difference and the color difference between adjacent pixels and to
determine regions corresponding to the large absolute values as
regions of the high contrast or the large color variation. For
example, the absolute value of difference between the L* data for
two points can be used as the concentration difference between the
two points. The square root of the sum of the squares of the
differences between the a*b* data for two points can be used as the
color difference between the two points.
[0131] The deposited ink corresponding to the following first
pixels or second pixels is actually subjected to the intensive
irradiation of the light. The first pixels are within the edge
regions and moreover have image concentration (such as the L*
value) more than a predetermined threshold value derived from a
predetermined bleeding potential estimated from the combination of
the ink characteristics and the recording medium characteristics.
The second pixels are adjacent to the first pixels. For instance,
the first pixels correspond to the portions whose L* values are
greater than the predetermined threshold value, above which the
bleeding of the ink is liable to occur, derived from the bleeding
potential determined on the basis of the properties of the ink and
the recording medium.
[0132] More specifically, the aforementioned filtering process is
carried out with respect to pixels in the range in which light can
be irradiated onto the deposited ink in one scanning operation, the
filtered values for the pixels are respectively determined, and a
histogram of the filtered values is made. Using this histogram, the
relevant pixels are taken to be those pixels which have the higher
filtered values and have the image concentration greater than the
threshold value, above which the bleeding is liable to occur,
derived from the bleeding potential determined on the basis of the
properties of the ink and the recording medium. The relevant pixels
are established starting from the pixel having the highest maximum
filtered value and continuing until the number of pixels that can
be irradiated in one scan being reached. Light is then intensively
irradiated onto the deposited ink in the region of these pixels
(the first pixels) and the adjacent pixels (the second pixels).
[0133] Moreover, as a simpler alternative, it is also possible to
adopt a method in which the filtered values for the pixels are
determined by carrying out the aforementioned filtering process
with respect to the pixels in the range in which light can be
irradiated onto the deposited ink in one scan, whereupon a
histogram of these filtered values is made. Then, using this
histogram, the light is intensively irradiated onto the deposited
ink in the region of the pixels (the first pixels) having higher
filtered values, starting from the highest filtered value of the
respective pixels and continuing until the number of pixels that
can be irradiated in one scan being reached, and the region of the
second pixels adjacent to the first pixels.
[0134] The definitions of L*a*b* are as described below by way of
example.
[0135] Japanese Standards Association: Japanese Industrial
Standards Handbook "Optics"
[0136] Color representation methods: L*a*b* representation scheme
and L*u*v* representation scheme
[0137] Standard number: JIS Z8729: 1994
[0138] FIGS. 12A, 12B and 12C show the Prewitt matrix, the Sobel
matrix and the Roberts matrix, respectively. The rotated matrices
are obtained by rotating the matrices shown in FIGS. 12A, 12B and
12C through 90.degree.. Edges in the longitudinal direction and in
the width direction are determined by means of the matrices shown
in FIGS. 12A, 12B and 12C and the rotated matrices.
[0139] The actual calculation is similar to a standard image
processing matrix calculation. It is possible to adopt the filtered
value obtained from the following calculation. An absolute value
may be determined for the sum of the products of "the target pixel
and the peripheral pixels around the target pixel" and the
corresponding components of the matrix being adopted. Then, the
larger of calculation results concerning the longitudinal direction
and the width direction may be taken as the filtered value for the
target pixel.
[0140] It should be understood, however, that there is no intention
to limit the invention to the specific forms disclosed, but on the
contrary, the invention is to cover all modifications, alternate
constructions and equivalents falling within the spirit and scope
of the invention as expressed in the appended claims.
* * * * *